Cytomegalovirus (CMV) is quite common in the population, and has been associated with mild to severe infections of neonates, mononucleosis and hepatitis in adults, Kaposi's sarcoma, and the newly described immunodeficiency syndrome (AIDS). The goals of the proposed research are to characterize cytotoxic reactivity of peripheral blood lymphocytes and monocytes during human CMV infection. The studies will focus on both immune recall of cytotoxic responses in vitro, and circulating, in vivo-generated cytotoxic reactivity in normal donors, CMV mononucleosis patients, renal transplant recipients receiving cyclosporin A, male homosexuals with prodromal AIDS, and AIDS patients. We propose to characterize the anti-CMV cytotoxic T lymphocyte responses, including HLA restriction, virus specificity, and comparison with natural killer cell, monocyte, and antibody-dependent cell cytotoxicity. Our hypothesis is that certain individuals, i.e., cyclosporin A-treated renal transplant recipients and prodromal AIDS patients, do not have the capacity to generate a strong cytotoxic T cell response to CMV infection, thereby predisposing them to serios direct and secondary effects of the virus. Finally, we propose to further analyze an unusual subset of suppressor T Lymphocytes that emerges during CMV mononucleosis for unique surface markers and functional chracteristics. We will produce monoclonal antibodies against the cells for use as a probe for these putative, new suppressor T cell determinants.